First documented in 1920 as "snapping head syndrome," the condition received more serious attention in 1989 when neurologist J.M.S. Pearce examined the clinical features of 50 patients dealing with the disorder:

[Although] some start in childhood . . . the commonest age of onset remains middle and old age . . . . The pattern of episodes of explosions is . . . variable. Some report two to four attacks followed by prolonged or total remission, others have more frequent attacks up to seven in one night, for several nights each week and may then remit for several months. . .

In 1991, Sachs & Svanborg made "polygraphic recordings [with] EEG, electro-oculograms, and submental electromyograms (DMB)" of six patients with some interesting results:

Five of the six cases who underwent daytime polysomnography slept during parts of the recording in stages 1-2. Only two reported attacks of explosions. One patient had two attacks while she was awake and relaxed . . . . In . . . her attacks there was . . . an alerting effect. The other case reported after the recording session that he had experienced an explosion during sleep. According to his EEG, he had not, in fact, slept at all during the recording. . . .

Concluding that topiramate lessened the intensity of EHS events but did not diminish its frequency, the study's authors noted that other helpful drug therapies have included clonesapam, nifedipine, flunarizine and clomipramnine. Drugs that have been unsuccessful in the treatment of EHS include amitriptyline, doxepin, trimipramine and citalopram.

A sudden movement of a middle ear component of the Eustachian tube, or perhaps a brief temporal lobe complex partial seizure (though EEG studies have generally been reported as normal). There is a correlation with stress or extreme fatigue. EHS has been linked to rapid withdrawal from benzodiazepines and selective serotonin reuptake inhibitors (SSRIs) (which our patient was not taking).

Bonus Facts:

--According to the Centers for Disease Control (CDC), between 50 and 70 million adults in the United States suffer from either a "sleep or wakefulness disorder."

--In a 2009 study of unhealthy and other sleep behaviours, of the nearly 75,000 adults surveyed, over 35 per cent slept less than seven hours each night. More shockingly: "37.9% reported unintentionally falling asleep during the day at least once in the preceding month, and 4.7% reported nodding off or falling asleep while driving at least once in the preceding month."